Patent GB-159147-A (GB)
Title: Improvements relating to electrical measuring, indicating or relay apparatus for polyphase circuits
IPC: G01R29/16
Filed: 1921-02-14
Abstract: 159,147. Metropolitan-Vickers Electrical Co., Ltd., (Assignees of Evans, R. D.). Feb. 13, 1920, [Convention date]. Electromagnetic switches. - Apparatus for indicating, measuring or being operated by the balanced polyphase components. either in current or voltage, of a polyphase electric circuit of given frequency comprises an alternating-current meter or relay connected to a stationary transformer which has windings connected to the circuit through resistances and reactances or impedances of such a nature as to produce in the windings a resultant value of ampere-turns substantially proportional to one component and independent of the other component. The use of the rotary apparatus described in Specification 159,148 is thus avoided. For measuring one balanced component of an unbalanced three-phase pressure, a voltmeter 5, Fig. 4, is connected to the secondary winding 6 of a transformer 7 having two primary windings 9, 10. The winding 9 is connected between the mains 2, 4 in series with a non- inductive resistance 12 of sufficiently high value to bring the current in the winding 9 substantially into phase with the pressure between the mains 2, 4. The winding 10 is connected between the mains 3, 4 in series with a reactance 13 and resistance 14 of such values that the current in the winding 10 is 60 degrees behind the pressure between the mains 3, 4. Currents due to one rotational component cause equal and opposite magnetic effects in the transformer 7 and consequently do not affect the voltmeter 5. Currents of the opposite phase sequence, due to the oppo-- sitely rotating component, induce currents in the secondary winding 6 proportional to this component of the unbalanced pressure. By reversing the connections to the mains 3, 4, the other rotational component may be measured. Fig. 2 shows an arrangement for measuring the rotational components of the currents. The primary windings 9, 10 of the transformer 7 are connected, through resistances 32, 34, to the secondary windings 30, 33. of current transformers connected in the mains. The secondary winding 33 is shunted by a reactance 37 and resistance 36; a resistance 35 may be connected in shunt to the winding 30. The values of the reactance 37 and resistances 35, 36 are so chosen that the currents in the primary windings 9, 10 are respectively in phase with one line current and 60 degrees removed from another line current. The effects of the currents due to one rotational component neutralize one another, the reading on the ammeter 29 being proportional to the other component. Arrangements similar to those described with reference to Figs. 2 and 4 may be applied to the pressure and current coils respectively of a wattmeter, and may be arranged to read either rotational component of either true or reactive power, the transformers then being energized by currents the vectorial resultants of which are respectively proportional to the balanced components of voltage and current of the same phase-sequence and independent of the components of opposite phase-sequence. The ammeter 29, Fig. 2, may be replaced by a quantity meter. Relays may be actuated by similar means. The Specification as open to inspection under Sect. 91 (3) (a) describes also modifications in which the transformer 7 is eliminated by the use of multiple-winding instruments with windings connected similarly to the windings 9, 10 of the transformer 7, and in which the impedances in the current-measuring arrangement in Fig. 2 are suitably modified, for instance, by replacing the reactance 37 by a resistance and the resistance 34 by a reactance and by omitting the resistance 35. This subject-matter does not appear in the Specification as accepted.